# How to estimate the timescale for strong interactions?

I have learned that the characteristic time for QCD process is about $10^{-24}s$, Then I wonder if there is a way to estimate the timescale for strong interactions?

• QCD is the theory of the strong interaction. May 13 '17 at 13:17

The width of a resonance is directly connected to the lifetime :

Γ=h_bar/τ Γ the width τ the mean life time

Thus, the lifetime of a particle is the direct inverse of the particle's resonance width. For example, the charged pion has the second-longest lifetime of any meson, at 2.6033×10^−8 s. Therefore, its resonance width is very small, about 2.528×10−8 eV or about 6.11 MHz.

That was classified as a weak interaction

The π0 which decays to two gamma has a lifetime of 8.4*10^-17 , and decays electromagnetically. It was classified as an electromagnetic interaction.

The charged rho meson has a very short lifetime, about 4.41×10^−24 s. Correspondingly, its resonance width is very large, at 149.1 MeV or about 36 ZHz.

That was classified as a strong interaction.

Thus the time scale of strong interactions can be extracted from the width of the resonances, of course corrected for experimental errors. For example the Higgs which decays weakly has a large width in the LHC measurements because of experimental errors. But in the beginning of classification of forces careful experiments measuring lifetimes were carried out.

That is how the interactions were classified as strong, weak and electromagnetic.

• Does this means the timescale of strong interaction is determined by the most short lifetime of the particle which take part in strong interaction？ May 14 '17 at 6:05
• It was the observation of different lifetimes in nuclear decays that classified the interactions as strong and weak and electromagnetic between them. Then a theory was developed, the standard model, which is consistent with this by assuming the strengths given in this table hyperphysics.phy-astr.gsu.edu/hbase/Forces/funfor.html. Nhttps://physics.stackexchange.com/#ow we can classify them according to the strength, by calculations,taking into account quantum numbers etc which might enhance or inhibit a lifetime. May 14 '17 at 7:22